Stax Lambda SR-L500 MK2 + SRM-500T: the purity of electrostatic technology

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Second version of the Stax Lambda SR-L500 released in 2016, the new Stax Lambda SR-L500 MK2 renews one of the most iconic models from the electrostatic headphone specialist. This new generation has a slightly revamped design to reduce resonance and distortion. Their detachable cable is also different, using silver-plated copper conductors to optimize the transmission of the sound signal. These new elements allow the Stax Lambda SR-L500 MK2 headphones to provide a more precise musicality across a very wide bandwidth ranging from 7Hz to 41kHz.

With their large electrostatic drivers, the headphones promise a more precise sound across a very wide bandwidth ranging from 7Hz to 41kHz.

Like all of the electrostatic driver models on the market, the Stax Lambda SR-L500 MK2 headphones require a specific headphone amp. For this review, we opted for the Stax SRM-500T, a hybrid model with transistor preamplification and a 6FQ7/6CG7 tube power stage. Can this Stax headphone and headphone amplifier pairing achieve the musical nirvana described by Stax headphone users for over 70 years?

The Stax SRM-500T headphone amplifier is a hybrid model with transistor preamplification and a tube power stage to get the best performance with electrostatic technology.

Stax Lambda SR-L500 MK2 + SRM-500T: packaging & accessories

As the Stax Lambda SR-L500 MK2 electrostatic headphones and Stax SRM-500T headphone amplifier are two separate items that can be used independently, they are each delivered in their respective boxes. The Stax Lambda SR-L500 MK2 headphones come with a 2.5m long detachable cable with a proprietary 5-pin connector. The Stax SRM-500T headphone amp comes with a power cable, an RCA to RCA cable and a user guide.

Stax Lambda SR-L500 MK2: presentation

Design 

The Stax Lambda SR-L500 MK2 headphones are the midrange model in the Japanese manufacturer’s Lambda series. They are situated between the Stax Lambda SR-L300 (€550) and Stax Lambda SR-L700 MK2 (€1,750). These three electrostatic headphones have an identical visual design inherited from the 1977 Stax SR-Σ. This design hasn’t changed much since the first model, with large rectangular earpieces whose perforated structure reveals the drivers. They are, however, a little more refined and now look a lot like 2003’s Stax SRS-3010 headphones. While this is the Lambda range’s signature look, it is slightly dated and could do with being refreshed, like that of the Stax SR-X9000, Stax SR-009S, Stax SR-009S and Stax Omega SR-007 MK2 high-end models.

The Stax Lambda SR-L500 MK2 headphones have a very similar design to that of their predecessor, with long earpieces through which the drivers are visible.

We can also criticize the fact that, despite their price, the Stax Lambda SR-L500 MK2 headphones have an unrefined design. The external shells, entirely made of plastic, do not look particularly solid. The headband, also made of polymer, seems more robust and rightly uses this material to maximize elasticity in order to adapt more easily to different head shapes. While we can fault the choice of plastic for its lack of elegance, we can’t take away the fact that it is very light, allowing these Stax headphones to weigh only 351 grams without the cable. This is extremely light for a pair of hi-fi headphones of this size. As a result, the Stax Lambda SR-L500 MK2 headphones are very comfortable and can be worn for hours.

The Stax Lambda SR-L500 MK headphones feature a predominantly plastic design to reduce weight and maximize comfort.

The Stax Lambda SR-L500 MK headphones’ comfort also comes from their large earpieces that effectively surround the ears, especially at the top and bottom. The padding is not particularly thick, but it is very soft to avoid any uncomfortable pressure. The imitation leather covering also ensures a soft and pleasant feel.

The Stax Lambda SR-L500 MK headphones’ earpieces are very comfortable, with moderately thick padding.

The Stax Lambda SR-L500 MK headphones can hardly be felt when worn due to a thick headband that effectively distributes the headphones’ weight of 351 grams. To ensure a perfect fit for all users, the height of this band can be adjusted thanks to sliding attachment on the polymer headband. The latter is very flexible, which makes it possible to easily extend the space between the two earpieces, while maintaining optimal wearing comfort. Lastly, the Stax Lambda SR-L500 MK headphones’ shells are each mounted onto a U-shaped aluminum structure that allows the earpieces to rotate +/- 10° and swivel up and down.

The Lambda SR-L500 MK headphones are very comfortable thanks to their wide leather headband, their second flexible polymer headband and their adjustable and tiltable earpieces.

Electrostatic drivers

Since the early 60s, the Japanese manufacturer Stax has excelled in the design of electrostatic drivers and was the first to use them in headphones. Therefore, it is only natural that the Stax Lambda SR-L500 MK2 headphones use these drivers, optimized to further refine the precision of the reproduction. Very complex to develop, the Stax Lambda SR-L500 MK2’s electrostatic drivers offer clear advantages. They do not work in the same way as traditional dynamic drivers. Instead of the usual coil driver, there is a sheet of mylar or polymer enclosed by two metal electrodes to which extremely high voltages are applied. The electrodes pull and push the sheet acting as a diaphragm under the influence of the electric current they receive. The vibrations generate an exceptionally pure sound, from the lows to the highs.

The Stax Lambda SR-L500 MK2 headphones’ electrostatic drivers also have the advantage of providing a large emissive surface. This allows for a more enveloping sound, enhanced immersion and a better low frequency reproduction. The thinness and low mass of the diaphragm ensures an outstanding transient response that is far superior to that of any traditional driver. Thanks to these properties, the Stax Lambda SR-L500 MK2 has a wide frequency response of 7Hz to 41kHz.

Thanks to their electrostatic drivers, the Stax Lambda SR-L500 MK2 headphones provide an outstanding transient response and a perfect reproduction of each nuance.

However, the remarkable musicality of electrostatic drivers requires the use of a specific headphone amplifier. No standard headphone amp can provide the necessary voltage needed to operate electrostatic headphones. With an impedance of 145,000 ohms for a bias voltage of 580V DC, the Stax Lambda SR-L500 MK2 headphones require a high current capacity to operate. To this end, the Japanese manufacturer offers several amplifiers for electrostatic headphones: Stax SRM-252S, Stax SRM-D50, Stax SRM-400S, Stax SRM-500T, Stax SRM-700T, Stax SRM-700S, Stax SRM-T8000, and even a portable headphone amplifier, the Stax SRM-D10. The Stax Lambda SR-L500 MK2 headphones can also be paired with HiFiMAN electrostatic amplifiers, such as the HiFiMAN Jade II Amplifier and the very high-end HiFiMAN Shangri-La Jr Amplifier and HiFiMAN Shangri-La Sr Amplifier.

With an impedance of 145,000 ohms and a bias voltage of 580V DC, the Stax Lambda SR-L500 MK2 headphones require an amplifier designed specifically for electrostatic headphones, such as the Stax SMR-500T we used for this test.

Detachable cable

In order to work with a Stax or HiFiMAN headphone amp specifically designed for electrostatic models, the Stax Lambda SR-L500 MK2 headphones use a detachable cable with a proprietary 5-pin connector. Designed to maximize signal transmission, this low capacitance cable uses six ultra-high purity copper conductors, with reduced strand interaction to limit distortion. A small amount of titanium is added by the manufacturer to optimize signal transmission while maximizing the cable’s resistance to twisting and handling. To connect to the earpieces, the cable is equipped with two detachable connectors that allow it to be replaced if needed by a longer model, such as the 5 meter-long Stax SRE-750H.

The Stax Lambda SR-L500 MK2 headphones use a detachable cable equipped with a proprietary 5-pin connector, compatible with both Stax and HiFiMAN headphone amplifiers.

Stax Lambda SR-L500 MK2: key specifications

  • Electrostatic drivers
  • Open-back design
  • Polymer diaphragm
  • Frequency response: 7Hz to 41kHz
  • Sensitivity: 101 dB
  • Impedance: 145 kOhms
  • Bias voltage: 580V DC
  • 2.5m detachable cable with 5-pin STAX connector
  • Weight (without cable): 351g

Stax SRM-500T: presentation

Design 

The Stax SRM-500T headphone amplifier has an elongated housing that is 37.5cm deep, 19.5cm wide and 10cm high. It uses high-quality materials, notably with a robust metallic chassis that provides good isolation against electromagnetic interference. The front panel features a thick plate in brushed aluminum, while the other sides of the amp benefit from a charcoal chassis. Darker paint droplets have been sprayed on the latter to bring texture and depth to the device. The combination is very harmonious and elegant. The Stax SRM-500T amplifier is ideally placed in a hi-fi cabinet, next to other electronics and sources.

vThe Stax SRM-500T headphone amp has an elongated format with a sturdy aluminum chassis that makes it robust and highly resistant to electromagnetic interference.

To achieve the best performance with electrostatic headphones, the Stax SRM-500T headphone amplifier has an entirely analog class A design. It all starts with a power supply stage that uses, in addition to the conventional power transformer dedicated to the high voltage circuit, a second power transformer newly designed for the low voltage circuit. The latter has optimized winding to maximize energy efficiency and ensure better performance as well as a more stable current to offer a more accurate sound reproduction. It is combined with a pre-amplifier that uses custom-made low noise MOSFET transistors. At the output, the Stax SRM-500T headphone amplifier features 6FQ7/6CG7 power tubes, which are well known among audiophiles. This hybrid design ensures a warm, natural and soft reproduction. With a maximum output voltage of 300V, the Stax SRM-500T amplifier can easily power the vast majority of electrostatic headphones from Stax and HiFiMAN.

The Stax SRM-500T electrostatic headphone amplifier incorporates a transistor preamplifier and a tube output stage to add warmth, softness and naturalness to the sound.

Connectors

On its front panel in between the power button and the large volume knob, the Stax SRM-500T headphone amplifier provides a double headphone output in the proprietary Stax 5-pin format. You can therefore easily connect your Stax and HiFiMAN headphones. 

Thanks to its double headphone output, the Stax SRM-500T amp can simultaneously power two pairs of Stax or HiFiMAN headphones.

The rear panel features the connectors, which include an unbalanced RCA input and a balanced XLR input. It is therefore possible to connect the sources of your choice, such as a CD player, a network player, an audio DAC or even a preamplified turntable. Lastly, an RCA output is also included so that you can use the Stax SRM-500T amp in between sources and a hi-fi system, for example.

The Stax SRM-500T headphone amplifier features an RCA input and an XLR input to connect to all of your sources, such as a CD/SACD player, a network player or a preamplified turntable, for example.

Stax SRM-500T: key specifications

  • Electrostatic headphone amplifier
  • Double headphone output
  • Hybrid amplification
  • Transistor preamplification
  • 6FQ7/6CG7 tube output stage
  • RCA and XLR inputs
  • Output voltage: 300V
  • Dimensions (WxHxD): 195 x 102 x 375mm

Stax Lambda SR-L500 MK2 + SRM-500T: listening conditions

We paired the Stax Lambda SR-L500 MK2 headphones with the SRM-500T hybrid amplifier which was plugged into a Taga Harmony PF-2000 filtered power strip. For the source, we used the Bluesound Node 2021 network player to listen to music shared over the local network via DLNA and to enjoy Hi-Res playlists on Qobuz and Tidal. It was connected using the RCA cables supplied with the Stax headphones. We also used a Teac CD transport and a Pathos DAC connected via XLR.

Stax Lambda SR-L500 MK2 + SRM-500T: listening impressions

Coupled with the Stax SRM-500T hybrid headphone amplifier; the Stax Lambda SR-L500 MK2 headphones provided a soft, balanced and warm sound. With the album Home by Rhye, the tracks, which blend soul, electronica and jazz, were delivered with purity and naturalness, plunging us into a comfortable cocoon. The singer’s ethereal and androgynous voice was embodied with great finesse. Each timbre was beautifully textured and benefited from a smooth and captivating aspect. Throughout the album, the singer invited us to travel through a vast and very well defined acoustic landscape.

The Stax Lambda SR-L500 MK2 headphones worked in perfect harmony with the Stax SRM-500T for a soft, refined and suave sound.

The extreme softness offered by the Stax Lambda SR-L500 MK2 headphones was a pure delight when listening to jazz, as highlighted by Stan Getz’ Jazz Samba Encore!. The richness of the midrange enhanced the saxophone, which was skilfully reproduced and seemed to materialize right in front of us, in the saxophonist’s hands. This instrument had a very distinct character, with numerous nuances and harmonics conveyed with richness and accuracy. The acoustic guitar and the percussion instruments had a beautiful clarity that effectively separated each note from the rest of the soundstage. The slightest details were audible, like the double bass whose reverb created a very appealing sense of closeness. This approach was also noticeable with the vocals, whose tonal quality was enchanting and produced a real feeling of intimacy.

The Stax Lambda SR-L500 MK2 headphones offered rich and soft mids that enhanced the saxophone.

The Stax Lambda SR-L500 MK2 headphones also managed to enhance classical music and opera pieces with which the electrostatic drivers ensured great verve. They managed to instantly reproduce the strongest attacks, while maintaining consistency, precision and a sense of detail. The different nuances never blended together, with timbres that were always distinct and natural. Bowing was enhanced by the transparency and clarity of the Stax Lambda SR-L500 MK2’s highs. The soundstage was beautifully spacious, adding breadth to the sound and almost perfectly portraying the acoustic ambience of the recording.

The Stax Lambda SR-L500 MK2 headphones’ electrostatic drivers displayed great energy, allowing them to accurately reproduce classical music and opera pieces.

The tonal balance offered by the Stax Lambda SR-L500 MK2 headphones was almost perfect. Like many electrostatic models, however, we could criticize their slight lack of depth and impact in the bass. With jazz, classical or acoustic music, this lack of extension was not very critical and did not hinder the experience offered by the Stax Lambda SR-L500 MK2 headphones. However, these Stax headphones may be frustrating for lovers of bass with electronic music and pop, where powerful bass is an essential element for a lively listening experience. Apart from these few instances, the other accomplishments of the Stax Lambda SR-L500 MK2 headphones more than make up for this slight lack of bass.

The Stax Lambda SR-L500 MK2 headphones offer good tonal balance, but can still lack depth and energy in the lows.

Stax Lambda SR-L500 MK2: compared to…

Koss ESP-950: available for €1,199 with a dedicated headphone amplifier, the Koss ESP-950 headphones also use electrostatic drivers. They offer the same advantages as the Stax model, namely a lively, pure and captivating reproduction, but with a slight lack of depth in the lows. However, the bass is a little more generous with the Koss ESP-950s thanks to reinforced isolation. However, the Stax Lambda SR-L500 MK2 are softer, more detailed and more refined overall. 

Focal Clear MG: sold for €1,499, the Focal Clear MG headphones use dynamic drivers equipped with a magnesium cone that features an M-shaped dome. These drivers offer a slightly more balanced reproduction, particularly in the lows that are more generous, deep and impactful. The Focal Clear MGs are very detailed, clear and transparent across the entire spectrum, but can’t compete with the fine details provided by the Stax Lambda SR-L500 MK2s, which are also a little more energetic during attacks. Lastly, while their design isn’t as luxurious and is a little outdated, the Stax Lambda SR-L500 MK2 headphones are more comfortable for long listening sessions. 

The Focal Clear MG headphones have a more modern and intricate design than the Stax Lambda SR-L500 MK2s, which primarily prioritize comfort.

Stax Lambda SR-L500 MK2 + SRM-500T: who are they for?

Due to their open-back design, the Stax Lambda SR-L500 MK2 headphones are meant to be used at home. They are aimed at the most demanding music lovers who mainly listen to music for which the depth of the bass is not a determining factor: classical music, jazz, world music, blues, folk, etc. With these genres, the association with the Stax SRM-500T hybrid amplifier is ideal for enjoying an even smoother and softer sound. However, the Stax Lambda SR-L500 MK2 headphones’ somewhat dated design does not make them a model of choice for those who enjoy design and attractive objects. However, their comfort makes you forget these few inconveniences. If you find other types of headphones uncomfortable, the Stax Lambda SR-L500 MK2 may be the perfect choice.

Combined with the Stax SMR-500T hybrid amplifier, the Stax Lambda SR-L500 MK2 headphones are an excellent solution for those looking to discover the performance electrostatic technology can offer.

Stax Lambda SR-L500 MK2 + SRM-500T: conclusion 

The Stax Lambda SR-L500 MK2 headphones do not impress with their design. Their predominantly plastic structure seems fragile and cheap, but once you put the Stax Lambda SR-L500 MK2 on, these drawbacks disappear thanks to their optimal and always pleasant comfort. The reproduction is a credit to the brand’s previous electrostatic headphones, with details delivered with finesse, articulation and energy. The excursion in the lows remains limited, but the Stax Lambda SR-L500 MK2 headphones have many other qualities to beautifully reproduce their preferred frequency ranges. Finally, the association with the Stax SRM-500T hybrid amplifier is ideal to optimize the naturalness and the richness of the mids, as well as the softness of the highs delivered by the Stax Lambda SR-L500 MK2. 

We liked:

  • The rich mids and highs
  • The suave and soft reproduction
  • The spacious soundstage

We would have liked:

  • A more modern and less “plasticky” design

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